putfield_quick_w exception mishandled

Name: joT67522 Date: 08/28/97



There is a bug in the virtual machine source file executeJava_p5.m4 . The handler
for the opcode putfield_quick_w increments the interpreter pc before checking for
an exception. If the bytecode is the last one in a try block, this will cause the pc not
to be found in the exception handler table in the event of an exception.

The original code from executeJava_p5.m4 is as follows:

    Def012(putfield_quick_w)
mov edx, DWORD PTR _cp$[esp]
mov ah, BYTE PTR [esi+1]
mov al, BYTE PTR [esi+2]
add esi, 3
mov eax, DWORD PTR [edx+eax*4]
mov edx, DWORD PTR [eax+fb_signature]
mov eax, [eax+fb_offset]
mov dl, BYTE PTR [edx]
cmp dl, SIGNATURE_LONG
je Lb($pqw_islong)
cmp dl, SIGNATURE_DOUBLE
je Lb($pqw_islong)
Verify(ebx,ne,0,NullPointer,SP(2))
mov ebx, DWORD PTR [ebx+o_obj]
mov [ebx+eax], ecx
xor eax, eax
Ld_opc(0)
Dispatch0
   Lb($pqw_islong):
mov edx, [edi-4]

It should be changed to:

    Def012(putfield_quick_w)
mov edx, DWORD PTR _cp$[esp]
mov ah, BYTE PTR [esi+1]
mov al, BYTE PTR [esi+2]
   ; DELETE add esi, 3
mov eax, DWORD PTR [edx+eax*4]
mov edx, DWORD PTR [eax+fb_signature]
mov eax, [eax+fb_offset]
mov dl, BYTE PTR [edx]
cmp dl, SIGNATURE_LONG
je Lb($pqw_islong)
cmp dl, SIGNATURE_DOUBLE
je Lb($pqw_islong)
Verify(ebx,ne,0,NullPointer,SP(2))
    ******* add esi, 3 ; *** ADD ******************************
mov ebx, DWORD PTR [ebx+o_obj]
mov [ebx+eax], ecx
xor eax, eax
Ld_opc(0)
Dispatch0
   Lb($pqw_islong):
  ******** add esi, 3 ; *** ADD ******************************
mov edx, [edi-4]

I came across this problem running the following Java program with a JIT compiler that chose not to compile main:

  class IntList
  {
      public IntList next;
      IntList( ){ next = null; }
  }

  public class test
  {
      public static void main(String args[])
      {
          IntList x = new IntList();
          try {
              x.next.next = x;
          } catch (NullPointerException f) {
              System.out.println( "caught exception" );
          }
      }
  }

The exception is not caught; a call stack is dumped instead.

The bug does not occur if a JIT compiler is not loaded, because UseLosslessOpcodes
gets set to FALSE and the putfield_quick opcode gets used instead of putfield_quick_w.
It does not occur if the JIT compiler compiles main because (obviously) the interpreter
does not run all.

You can make the same bug occur if you either build a "null" JIT compiler or just go
into the JVM code and force the global UseLosslessOpcodes to TRUE.



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